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参数资料
| 型号： | L7980A |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 稳压器 |
| 英文描述： | 3.5 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封装： | ROHS COMPLIANT, HSOP-8 |
| 文件页数： | 10/44页 |
| 文件大小： | 1247K |
| 代理商： | L7980A |
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Application informations
L7980
18/44
Doc ID 15181 Rev 3
6.3
Output capacitor selection
The current in the capacitor has a triangular waveform which generates a voltage ripple
across it. This ripple is due to the capacitive component (charge or discharge of the output
capacitor) and the resistive component (due to the voltage drop across its ESR). So the
output capacitor has to be selected in order to have a voltage ripple compliant with the
application requirements.
The amount of the voltage ripple can be calculated starting from the current ripple obtained
by the inductor selection.
Equation 12
Usually the resistive component of the ripple is much higher than the capacitive one, if the
output capacitor adopted is not a multi layer ceramic capacitor (MLCC) with very low ESR
value.
The output capacitor is important also for loop stability: it fixes the double LC filter pole and
the zero due to its ESR. In Chapter 6.4, it will be illustrated how to consider its effect in the
system stability.
For example with VOUT=5 V, VIN=24 V, ΔIL=0.6 A (resulting by the inductor value), in order to
have a
ΔV
OUT=0.01VOUT, if the multi layer ceramic capacitor are adopted, 10 F are needed
and the ESR effect on the output voltage ripple can be neglected. In case of not negligible
ESR (electrolytic or tantalum capacitors), the capacitor is chosen taking into account its
ESR value. So in case of 220 with ESR=50 m
Ω, the resistive component of the drop
dominates and the voltage ripple is 33 mV
.
The output capacitor is also important to sustain the output voltage when a load transient
with high slew rate is required by the load. When the load transient slew rate exceeds the
system bandwidth the output capacitor provides the current to the load. So if the high slew
rate load transient is required by the application the output capacitor and system bandwidth
have to be chosen in order to sustain the load transient.
In the table below some capacitor series are listed.
Table 8.
Output capacitors
Manufacturer
Series
Cap value (
μF)
Rated voltage (V)
ESR (m
Ω)
MURATA
GRM32
22 to 100
6.3 to 25
< 5
GRM31
10 to 47
6.3 to 25
< 5
PANASONIC
ECJ
10 to 22
6.3
< 5
EEFCD
10 to 68
6.3
15 to 55
SANYO
TPA/B/C
100 to 470
4 to 16
40 to 80
TDK
C3225
22 to 100
6.3
< 5
ΔV
OUT
ESR
ΔI
MAX
ΔI
MAX
8C
OUT
f
SW
-------------------------------------
+
=
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相关代理商/技术参数 |
参数描述 |
|---|---|
| L7980ATR | 功能描述:直流/直流开关转换器 2 A Step-Down Reg 4.5V to 28V 250 kHz RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| L7980TR | 功能描述:直流/直流开关转换器 2A DC 4.5 V to 28 V Adj 0.6V 250 kHz RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| L7981 | 功能描述:直流/直流开关调节器 3A Step-Down Reg 3A DC 4.5-28V 250Khz RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| L7981A | 制造商:STMicroelectronics 功能描述:POWER CONVERSION - Rail/Tube 制造商:STMicroelectronics 功能描述:3A Step-Down Reg 3.7A 4.5 to 28V 1MHz 制造商:ST 功能描述:3A STEP-DOWN SWITCHING REGULATOR |
| L7981ATR | 功能描述:直流/直流开关调节器 3 A Step-Down Reg 4.5V to 28V 250 kHz RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
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